Allied agents go behind enemy lines to destroy a German missile base.

Allied Intelligence in London in December of 1942 receives reports that the Germans are developing long-range rockets. Though key advisers such as Professor Lindemann are skeptical of the reports, Prime Minister Churchill appoints Duncan Sandys, deputy supply minister, to head an investigation studying photographs for clues and pinpointing possible enemy launching sites. Then, when V-1 robot bombs begin to fall on London, three agents--Lieut. John Curtis, Phil Bradley, and Robert Henshaw--parachute into Holland and cross into Germany to infiltrate the underground plant at Peenemünde. They are posing as German agents known by the Allies to be deceased, but Henshaw is recognized by Gestapo agent Bamford and dies without giving any information. Curtis is confronted by the wife of the man he is impersonating. He locks her in his room and exacts her promise of secrecy; but she is ruthlessly killed by Frieda, an underground leader, to avoid any possible security leak. Bradley and Curtis get jobs at Peenemünde and transmit their findings to London. When London decides to bomb the site before long-range rockets can be launched, the agents are instructed to light the way for a squadron of Allied bombers. At the cost of their lives the two men make possible the total destruction of the Nazi installation.